I have a Briggs & Stratton ELS500 17.5hp engine (Model
31L777 0036E1) on a Simplicity rider. I
had an issue with oil coming out around the fuel pump and smoke coming out of
exhaust right after I changed the starter, so it makes me think the cause is
not the traditional problem (head gasket).
Here is what happened and I would like some advice.

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The previous owner of my rider had a Briggs ELS500
engine put on the rider due to an engine failure. So it is not original engine on the rider.

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The new engine fits more snugly against and
underneath the fuel tank area/metal frame than the original engine. SEE ATTACHED PIC.

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When the starter failed, I could not remove the plastic cover of the engine to get at the starter cleanly since the engine/cover is
tucked underneath the fuel tank area, and there is not enough room to pull up the cover where the fuel tank/frame is.

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So I kind of pried up on the front of the
plastic engine cover to just get enough room to pull the starter out. There was probably some binding going on where
the plastic cover fits underneath the fuel tank area and where the fuel pump
is since I applied a good amount of force during the lifting.

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After replacing the starter, I was using the
rider for about ten minutes when the engine started to smoke and oil was coming
out from the fuel pump area.

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So just because of the coincidence to applying
some force while lifting up the cover during the starter change, I am
suspecting this caused something to happen.
It just seems unlikely this job of replacing the starter is coincidental
with head gasket going bad.

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I removed and checked the hose going from the
oil fill tube to fuel pump. Looks in
perfect shape, so I did not damage that by lifting the cover.

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Any ideas on what I could have damaged?

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Could it be a breather, but I do not know where
that is located on this engine as the parts diagram does not show location?

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Here is parts diagram of the engine. http://www.powermowersales.com/p/Cub-Cadet-Parts?aribrand=CUT&user_credentials=2sZjaQLsSs4njvxQbV#/Briggs_%26_Stratton/31L777-0036-E1/Camshaft%2c_Crankshaft%2c_Cylinder%2c_Engine_Sump%2c_Gasket_Set_-_Engine%2c_Lubrication%2c_Operator%27s_Manual%2c_Piston%2c_Rings%2c_Connecting_Rod%2c_Warning_Label/31L7770036E1/50700002

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In the meantime, I am going to perform some
structural changes to the metal frame that holds the fuel tank such that I can
remove the plastic cover from the engine.
Then I can do a more thorough inspection.

I a thinking it is not a head gasket just because of the coincidence with changing the starter and using some force on lifting the engine plastic cover. Any help would be appreciated on ideas to suspected problems or troubleshooting.